Implement Phases 1-5: skeleton, OAuth, categories, video sync/feed, playback

- FastAPI + PostgreSQL + Alembic + React/Vite skeleton, Docker Compose, healthcheck
- Google OAuth (single allowed account), encrypted refresh token storage
- Subscriptions sync with pagination, uploads playlist batch fetch
- Categories CRUD, many-to-many channel assignment, category filtering
- Video sync (playlistItems + videos.list batching), cached feed with cursor
  pagination, background scheduler (APScheduler)
- Video detail page with YouTube embed player
- SPA fallback routing, optimistic UI updates, client-side query caching

40 backend tests covering OAuth allow-list, sync idempotency, cascade deletes,
cursor pagination, and category filtering.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_categories.py

@@ -0,0 +1,119 @@
+import pytest
+from fastapi.testclient import TestClient
+
+from app.core.auth_dependency import require_session
+from app.db import get_db
+from app.main import app
+from app.models.channel import Channel
+
+
+@pytest.fixture
+def client(db_session):
+    def _get_db_override():
+        yield db_session
+
+    app.dependency_overrides[get_db] = _get_db_override
+    app.dependency_overrides[require_session] = lambda: None
+    with TestClient(app) as test_client:
+        yield test_client
+    del app.dependency_overrides[get_db]
+    del app.dependency_overrides[require_session]
+
+
+def _create_channel(db_session, youtube_channel_id="chanA", title="Channel A"):
+    channel = Channel(youtube_channel_id=youtube_channel_id, title=title, subscribed=True)
+    db_session.add(channel)
+    db_session.commit()
+    db_session.refresh(channel)
+    return channel
+
+
+def test_category_crud(client):
+    created = client.post("/api/categories", json={"name": "Linux"}).json()
+    assert created["name"] == "Linux"
+    assert created["slug"] == "linux"
+    assert created["channel_count"] == 0
+
+    listed = client.get("/api/categories").json()
+    assert len(listed) == 1
+
+    updated = client.patch(f"/api/categories/{created['id']}", json={"name": "Linux/BSD"}).json()
+    assert updated["name"] == "Linux/BSD"
+
+    resp = client.delete(f"/api/categories/{created['id']}")
+    assert resp.status_code == 204
+    assert client.get("/api/categories").json() == []
+
+
+def test_category_name_must_be_unique(client):
+    client.post("/api/categories", json={"name": "Шахматы"})
+    resp = client.post("/api/categories", json={"name": "шахматы"})
+    assert resp.status_code == 409
+
+
+def test_cyrillic_slug_transliterated(client):
+    created = client.post("/api/categories", json={"name": "Научпоп"}).json()
+    assert created["slug"] == "nauchpop"
+
+
+def test_delete_category_does_not_delete_channel(client, db_session):
+    channel = _create_channel(db_session)
+    category = client.post("/api/categories", json={"name": "IT"}).json()
+
+    client.put(f"/api/channels/{channel.id}/categories", json={"category_ids": [category["id"]]})
+    client.delete(f"/api/categories/{category['id']}")
+
+    resp = client.get(f"/api/channels/{channel.id}").json()
+    assert resp["id"] == channel.id
+    assert resp["category_ids"] == []
+
+
+def test_channel_can_belong_to_multiple_categories(client, db_session):
+    channel = _create_channel(db_session)
+    cat1 = client.post("/api/categories", json={"name": "Linux"}).json()
+    cat2 = client.post("/api/categories", json={"name": "IT"}).json()
+
+    resp = client.put(
+        f"/api/channels/{channel.id}/categories",
+        json={"category_ids": [cat1["id"], cat2["id"]]},
+    ).json()
+
+    assert sorted(resp["category_ids"]) == sorted([cat1["id"], cat2["id"]])
+
+
+def test_assign_unknown_category_rejected(client, db_session):
+    channel = _create_channel(db_session)
+    resp = client.put(f"/api/channels/{channel.id}/categories", json={"category_ids": [9999]})
+    assert resp.status_code == 400
+
+
+def test_channels_filter_by_category_and_uncategorized(client, db_session):
+    channel_a = _create_channel(db_session, "chanA", "Channel A")
+    channel_b = _create_channel(db_session, "chanB", "Channel B")
+    category = client.post("/api/categories", json={"name": "Linux"}).json()
+    client.put(f"/api/channels/{channel_a.id}/categories", json={"category_ids": [category["id"]]})
+
+    in_category = client.get(f"/api/channels?category_id={category['id']}").json()
+    assert [c["id"] for c in in_category] == [channel_a.id]
+
+    uncategorized = client.get("/api/channels?uncategorized=true").json()
+    assert [c["id"] for c in uncategorized] == [channel_b.id]
+
+
+def test_reorder_categories(client):
+    cat1 = client.post("/api/categories", json={"name": "A"}).json()
+    cat2 = client.post("/api/categories", json={"name": "B"}).json()
+    cat3 = client.post("/api/categories", json={"name": "C"}).json()
+
+    reordered = client.post(
+        "/api/categories/reorder",
+        json={"category_ids": [cat3["id"], cat1["id"], cat2["id"]]},
+    ).json()
+
+    assert [c["id"] for c in reordered] == [cat3["id"], cat1["id"], cat2["id"]]
+
+
+def test_reorder_rejects_mismatched_ids(client):
+    client.post("/api/categories", json={"name": "A"})
+    resp = client.post("/api/categories/reorder", json={"category_ids": [9999]})
+    assert resp.status_code == 400